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  #1  
Old 01-09-2003, 06:15 PM
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Question Timing Chain Replacement Intervals For Diesels?

What is the "recommended" interval for timing chain replacement for the '87 6 cyl, the 5 cyl turbo and the 240 diesels? Thanks Chris
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Old 01-09-2003, 06:30 PM
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It is all based on oil changes. If the oil changes have been regular - 3k miles/dino then I would not expect to see a timing chain go for less than 250k miles for the W123 models. It is pretty easy to check the amount of stretch.
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Old 01-09-2003, 09:19 PM
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There's a service bulletin( it's a few years old )concerning timing chain stretch on your 87' 6cyl. 603. The chain should be replaced at 5 degrees of stretch. If it stretches 10 degrees you could have some major problems! This forum has loads of info on 116/117 timing chain issues, but believe me, you ain't seen nothin' until you've seen a 603 chain break!!!. It breaks the camshaft into six pieces, bends most of the valves, and due to valve train geometry, often damages the cylinder head beyond repair. I've also seen the injection pump gear, front engine cover and chain oiling nozzle damaged as well. The good news is that it's easy to check the amount of stretch. Just remove the boost cross-over pipe and valve cover and line up the marks. The amount of stretch can be read on the front balancer.
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Old 01-09-2003, 10:29 PM
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ILUVMLS, thanks for the heads up on the 603. A client of mine bought this '87 with 193,00 mi on it and I don't think that it has ever had a chain replaced. So with the cam lined up,you ck the ballancer for the amount of stretch? Does itread out on the timing marks?

engatwork, does the same procedure for the 603 eng work on the 617 and 615 engines? Chris
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Old 01-10-2003, 02:47 AM
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Quote:
Originally posted by ILUVMILS
There's a service bulletin( it's a few years old )concerning timing chain stretch on your 87' 6cyl. 603. The chain should be replaced at 5 degrees of stretch. If it stretches 10 degrees you could have some major problems! This forum has loads of info on 116/117 timing chain issues, but believe me, you ain't seen nothin' until you've seen a 603 chain break!!!. It breaks the camshaft into six pieces, bends most of the valves, and due to valve train geometry, often damages the cylinder head beyond repair. I've also seen the injection pump gear, front engine cover and chain oiling nozzle damaged as well. The good news is that it's easy to check the amount of stretch. Just remove the boost cross-over pipe and valve cover and line up the marks. The amount of stretch can be read on the front balancer.
What would running a car with 10 degrees advance do to the engine? Is it possible there would be no damage?
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Old 01-10-2003, 07:22 AM
LarryBible
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Thanks ILUVMILS. There are many people who know that they must change timing BELTS as a preventive maintenance item at a specified mileage to be safe. From that, it is natural for them to think the same is true for a timing CHAIN. Stretch is a key and close inspection of other components such as tensioner and rails may even be more important.

Even a stretched chain usually won't break unless something causes it to break such as a rail breaking off and hanging up the works.

To check for stretch with the valve cover off I turn the engine with the harmonic balancer bolt until the cam mark is nearing the bearing stand mark then start turning the engine as slowly as possible until the cam mark is aligned, then look at the harmonic balancer mark, if it is NOT at TDC, or extremely close, I am comfortable.

This is NOT the correct chain stretch measurement method, however. To do it properly you need a dial indicator and the exact procedure for YOUR particular engine. It involves measuring valve lift and associating that with crankshaft position. This is much more precise.

If it is on my own engine that I am personally inspecting over the years, then it is all relative. I know that the marks aligned properly when it was a young engine, so I can tell if there is any noticable stretch by aligning the marks.

As engatwork pointed out, if you change oil and filter frequently your timing chain wear will in all likelihood be minimal to nonexistent. If you go by MB recommended oil change interval, there will be microscopic particulate in the oil that will wear the chain.

BTW when we talk about stretch, this is a misleading term. The steel links of the chain do not STRETCH. It is the rollers and pins that wear. Since there are so many links in the chain, even a half thousandth of wear on each link would add up to significant "stretch" of the chain.

If an engine ran with 10 degrees of chain stretch and did not break, there would be no damage to the engine, it just wouldn't run well. It would be time to change the chain, probably the tensioner, depending on the engine model and certainly inspect the rails.

Have a great day,
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  #7  
Old 01-10-2003, 01:16 PM
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I check chains for stretch on all later 5 and 6 cly diesels fairly often after 120k. Replace after 10 deg's and its much easier to check them with the led tool for the pump.



Joe
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  #8  
Old 01-10-2003, 05:08 PM
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joe p....Led tool?

Is the led tool a timing tool used for MBZ? What does it do and how does it work? Chris
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  #9  
Old 01-10-2003, 08:22 PM
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The Service Bulletin I mentioned cited complaints of hard starting, rough running, and smoke/no power. Larry Bibles' description of checking chain stretch is right on the money, however MB says that reading the degree marks on the balancer is conclusive enough to decide whether or not to replace the chain. I'm not sure what the diffrence is, but I've replaced dozens of 603 chains, but I've yet to see a bad 602/601 chain. Probably the same chain set-up, but the 4 and 5 cylinders are less taxing on the chain. Aside from the the chain stretch issue, I've yet to see a bottom end failure of any kind on the 603, even at 400K+. It's a well built motor capable of exceptionally long life. With that said, my favorite is still the 617.
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